Recently, in medical fields, identification codes designating company names and/or product names have been added to front faces of tablets in order to prevent medical accidents such as mis-preparation of medicines by pharmacists and taking medicines erroneously by patients. Conventionally, addition of identification codes to tablets was carried out by means of stamping, transcription, or the like.
Stamping is a method for imprinting on a surface of a tablet by compressive forming with a carved punch when forming powder or granule into the tablet by a tablet press. Such a stamping is mainly used for uncoated tablets and film-coated tablets. However, in the event that the punch does not leave the tablet smoothly due to pharmaceutical formulation and powder or granule properties when the punch presses against the surface of the tablet in compressive forming, a part of imprint is sometimes left out and thus stamping could not imprint a complicated shape clearly. Also, in the case of film-coated tablets, since the tablets are coated after imprinting, imprints tend to be blurred and thus readability was poor.
On the other hand, transcription is a printing method for pressing a surface of a tablet with a transfer roller. According to transcription, in the case of a film-coated tablet with a smooth coated surface and a sugar-coated tablet with a sugar coating, clear print is available. However, in the case of a film-coated tablet with an unsmooth coated surface, printing tends to be smeared and blurred, and in the case of an uncoated tablet, a printing failure sometimes occurs because the uncoated tablet has properties of absorbing ink and there is powder attached on a surface of the uncoated tablet. Also, tablets need to be positioned one by one in a pocket of a printing apparatus, and thus clogging of the pocket often occurs. Further, in the case of an R tablet with a round surface, since the transfer roller contacts a limited area of the round surface of the R tablet and printing thus needs to be carried out in a small area, the size of printed letters becomes small and readability was poor.
Accordingly, in a contact printing style such as a prior-art tablet press or transcription-style printing apparatus in which a punch or transfer roller is pressed against a tablet, imprinting failures or printing failures occurred, thus making yield rate of products worse, which became a factor of deteriorating the quality of the products. Also, each time an identification code changes an expensive punch or transfer roller needs to be changed, thus increasing cost. Therefore, there was a strong demand for a contactless-printing that can contactless-print on tablets without causing damages on the tablets and that can also change identification codes inexpensively and easily.
On the other hand, as a contactless printing style, laser printing on tablets is known in the art. However, for laser printing, if tablets do not contain titanium oxide, color of a printing portion cannot appear. In the case of a film-coated tablet or sugar-coated tablet, it contains titanium oxide on a surface thereof and thus color of print can appear, but in the case of an uncoated tablet, it does not contain titanium oxide and thus it was difficult to indicate color of print by laser printing.
Accordingly, the applicant of the present application proposed a printing apparatus that can contactless-print on a work-piece (or tablet) by a method other than a laser printing (see paras. [0035] to [0038] and FIGS. 1, 2, 4 of Japanese patent application publication No. 2011-20325).
This printing apparatus is comprised of a supplying unit to supply works (or tablets) successively, a conveyor to randomly convey the works supplied by the supplying unit, a CCD camera to detect and photograph the works introduced in a predetermined area, and an inkjet printer to print on the works during conveyance of the conveyor based on work information by the CCD camera.
In this case, since print process is carried out by injection of ink on a surface of the work by the inkjet printer, contactless-printing on the tablet can be achieved. As a result, not only for film-coated tablets and sugar-coated tablets but also for uncoated tablets, clear printing is available. Also, in this case, printing failures resulting from contact with a tablet do not occur, thus improving yield rate of the products. Further, since it can readily react to changes of identification codes including variable information such as expiration date, manufacturing number, and the like, thus reducing cost.
Moreover, even in the event that positions, orientations and faces of supplied tablets are not equal but random, print process of the tablets is carried out by detecting the positions, orientations and faces of the tablets based on images captured by the CCD camera, thus eliminating the necessity for positioning the tablets one by one and allowing for a plurality of tablets to be processed all together. Thereby, printing can be efficiently processed and high speed process is available.
In the printing apparatus mentioned above, when it detects a defective tablet (also sometimes called simply “a defective” herein) after the printing process and rejects the defective, the defective needs to be picked up with pinpoint accuracy among a large number of tablets disposed randomly on the conveyors. However, in the above-mentioned printing apparatus, since a large number of tablets supplied are disposed at a random spacing on the conveyors not only in a longitudinal conveyance direction but also in a lateral width direction perpendicular to the longitudinal conveyance direction, it is difficult to reject only the defective tablet with pinpoint accuracy.
The present invention has been made in view of such conventional circumstances and the problem which the present invention aims to resolve is to provide a tablet printing apparatus that can contactless-print on tablets supplied successively and randomly and that can reject only defective tablets securely with pinpoint accuracy.